The invention relates generally to diagnostic imaging and particularly, to a system and method of obtaining monochromatic representations of images at different energy levels.
Imaging systems such as general radiography X-ray system, tomosynthesis system, computed tomography (CT) system, mammography, positron emission tomography (PET) system, ultrasonic imaging, nuclear medicine imaging system and various other modalities are used to create images of a patient or object. These images are based on the attenuation of radiation passing through the object. Further, these imaging modalities may be used for contrast enhancement, volume reconstructions, two-dimensional image formation and so forth.
Typically, X-ray imaging systems for both medical and non-medical applications, utilize an X-ray tube to generate X-rays for the imaging process. In particular, conventional single rotating-anode X-ray tubes, which have single emission point that illuminates the entire field of view simultaneously, are typically employed as a source of X-rays in X-ray based imaging systems. Emitted X-rays pass through the object to expose the film, and the degree of exposure at the various points on the film are largely determined by the density of the object along the path of the X-rays. It is now common to utilize solid-state digital X-ray detectors (e.g., an array of switching elements and photo-sensitive elements such as photodiodes) in place of film detectors. The charges generated by the X-rays on the various points of the detector are read and processed to generate a digital image representative of attenuation of the object in electronic form, that are then transmitted to the data processing system for image reconstruction.
CT imaging system may include dual energy (DE), multienergy (ME), and/or energy discriminating (ED) CT imaging system. Dual energy imaging in digital X-ray combines information from two sequential exposures at different energy levels. Multienergy imaging systems may have the energy spectra from different X-ray tube captured as a series of images in a rapid sequence. The EDCT, MECT, and/or DECT imaging system are examples configured to be responsive to different X-ray spectra. The detected signals from the spectrum of two regions of photon energy provide sufficient information to resolve the energy dependence of the material being imaged. However the images are processed to separate materials having varying atomic numbers and densities, using known methods.
In certain applications, for example dual energy X-ray or CT imaging system, the images acquired may have a similar CT number. CT number is defined as a quantitative scale for describing the relative transparency of the object to the passage of X-rays. During such instances, basis material decomposition (BMD) may be used for differentiating the material components in the images. However, it is noted that the images constructed through BMD techniques usually elevate noise component in the images.
BMD component combination technique is a method that has reduced noise components at a given energy range, where linearly weighted combination of the two BMD material images produces images in virtual monochromatic representation. Such monochromatic images can be reformed at any incident X-ray photon energy, for example from 10s to a few 100s of Kilo electron volt (keV). However, while using these reformed monochromatic images at lower keV or high keV, the noise components can be substantially high in these images.
Therefore, it is desirable to obtain monochromatic images from X-ray digital radiography systems or CT systems, at a wide range of energy levels and with reduced noise components.